LF: LPF inductor cores possible cause?

["J. Allen" <vy1ja@northwestel.net>]

Jim and All,

Thanks for the good explanation.  The spikes are displayed on the scope 
which is connected to the ScopeMatch and are on both the voltage and current 
traces.
The scopematch pickup has a half meter section of coax between it and the 
LPF, which in turn has an even shorter coax jumper connecting it to the amp 
output. The LPF  uses two single-layer, air-core, solenoid inductors mounted 
at right angles to each other.
Your comments raised a set of questions:

Could it be that the single 640 FET amp and this Push Pull amp with 2 640 
are such different designs that the air core inductor LPF which works well 
with one, does not work with the other?
Is it possible that some odd inductive or capacitive coupling lets those 
high frequency spikes  be generated?
If this is the cause of the spikes, will it require a pair of  toroid cores, 
or will a pair of TV cores suffice?
Order toroid cores,  yes or no?

Thanks,

J.